Introduction to MySQL

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Road Map

Introduction to MySQL Connecting and Disconnecting Entering Basic Queries Creating and Using a Database

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MySQL

MySQL is a very popular, open source database. Officially pronounced “my Ess Que Ell” (not my

sequel). Handles very large databases; very fast

performance. Why are we using MySQL?

Free (much cheaper than Oracle!) Each student can install MySQL locally. Easy to use Shell for creating tables, querying tables, etc. Easy to use with Java JDBC

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Using a Database

To create a new database, issue the “create database” command: mysql> create database webdb;

CREATE DATABASE bookinfo; 

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Creating a Table

Once you have selected a database, you can view all database tables:

mysql> show tables;Empty set (0.02 sec) An empty set indicates that I have not

created any tables yet.

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Creating a Table

Let’s create a table for storing pets. Table: pets

ID: INT(8)name: VARCHAR(20)owner: VARCHAR(20)species: VARCHAR(20)sex: CHAR(1)birth: DATEdate: DATEPrimary Key (ID);

VARCHAR isusually usedto store stringdata.

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Creating a Table

To create a table, use the CREATE TABLE command:

mysql> CREATE TABLE pet ( -> name VARCHAR(20), -> owner VARCHAR(20), -> species VARCHAR(20), -> sex CHAR(1), -> birth DATE, death DATE);Query OK, 0 rows affected (0.04 sec)

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Showing Tables

To verify that the table has been created:mysql> show tables;+------------------+| Tables_in_test |+------------------+| pet |+------------------+1 row in set (0.01 sec)

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Deleting a Table

To delete an entire table, use the DROP TABLE command:

mysql> drop table pet;Query OK, 0 rows affected (0.02 sec)

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Loading Data

Use the INSERT statement to enter data into a table.

For example:

INSERT INTO pet VALUES ('Fluffy','Harold','cat','f','1999-02-04',NULL);

The next slide shows a full set of sample data.

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More data…

name owner species sex birth death

Fluffy Harold cat f 1993-02-04

Claws Gwen cat m 1994-03-17

Buffy Harold dog f 1989-05-13

Fang Benny dog m 1990-08-27

Bowser Diane dog m 1998-08-31 1995-07-29

Chirpy Gwen bird f 1998-09-11

Whistler Gwen bird 1997-12-09

Slim Benny snake m 1996-04-29

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SQL Select

The SELECT statement is used to pull information from a table.

The general format is:

SELECT what_to_selectFROM which_table WHERE conditions_to_satisfy

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Selecting All Data

The simplest form of SELECT retrieves everything from a table

mysql> select * from pet;+----------+--------+---------+------+------------+------------+| name | owner | species | sex | birth | death |+----------+--------+---------+------+------------+------------+| Fluffy | Harold | cat | f | 1999-02-04 | NULL || Claws | Gwen | cat | f | 1994-03-17 | NULL || Buffy | Harold | dog | f | 1989-05-13 | NULL || Fang | Benny | dog | m | 1999-08-27 | NULL || Bowser | Diane | dog | m | 1998-08-31 | 1995-07-29 || Chirpy | Gwen | bird | f | 1998-09-11 | NULL || Whistler | Gwen | bird | | 1997-12-09 | NULL || Slim | Benny | snake | m | 1996-04-29 | NULL |+----------+--------+---------+------+------------+------------+8 rows in set (0.00 sec)

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Selecting Particular Rows

You can select only particular rows from your table.

For example, if you want to verify the change that you made to Bowser's birth date, select Bowser's record like this:

mysql> SELECT * FROM pet WHERE name = "Bowser";+--------+-------+---------+------+------------+------------+| name | owner | species | sex | birth | death |+--------+-------+---------+------+------------+------------+| Bowser | Diane | dog | m | 1998-08-31 | 1995-07-29 |+--------+-------+---------+------+------------+------------+1 row in set (0.00 sec)

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Selecting Particular Rows

To find all animals born after 1998SELECT * FROM pet WHERE birth >= "1998-1-1";

To find all female dogs, use a logical ANDSELECT * FROM pet WHERE species = "dog" AND sex = "f";

To find all snakes or birds, use a logical ORSELECT * FROM pet WHERE species = "snake" OR species = "bird";

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Selecting Particular Columns

If you don’t want to see entire rows from your table, just name the columns in which you are interested, separated by commas.

For example, if you want to know when your pets were born, select the name and birth columns.

(see example next slide.)

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Selecting Particular Columns

mysql> select name, birth from pet;+----------+------------+| name | birth |+----------+------------+| Fluffy | 1999-02-04 || Claws | 1994-03-17 || Buffy | 1989-05-13 || Fang | 1999-08-27 || Bowser | 1998-08-31 || Chirpy | 1998-09-11 || Whistler | 1997-12-09 || Slim | 1996-04-29 |+----------+------------+8 rows in set (0.01 sec)

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Sorting Data

To sort a result, use an ORDER BY clause. For example, to view animal birthdays, sorted by

date:mysql> SELECT name, birth FROM pet ORDER BY birth;+----------+------------+| name | birth |+----------+------------+| Buffy | 1989-05-13 || Claws | 1994-03-17 || Slim | 1996-04-29 || Whistler | 1997-12-09 || Bowser | 1998-08-31 || Chirpy | 1998-09-11 || Fluffy | 1999-02-04 || Fang | 1999-08-27 |+----------+------------+8 rows in set (0.02 sec)

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Sorting Data

To sort in reverse order, add the DESC (descending keyword)

mysql> SELECT name, birth FROM pet ORDER BY birth DESC;+----------+------------+| name | birth |+----------+------------+| Fang | 1999-08-27 || Fluffy | 1999-02-04 || Chirpy | 1998-09-11 || Bowser | 1998-08-31 || Whistler | 1997-12-09 || Slim | 1996-04-29 || Claws | 1994-03-17 || Buffy | 1989-05-13 |+----------+------------+8 rows in set (0.02 sec)

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Working with NULLs

NULL means missing value or unknown value.

To test for NULL, you cannot use the arithmetic comparison operators, such as =, < or <>.

Rather, you must use the IS NULL and IS NOT NULL operators instead.

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Working with NULLs

For example, to find all your dead pets (what a morbid example!)

mysql> select name from pet where death >IS NOT NULL;

+--------+| name |+--------+| Bowser |+--------+1 row in set (0.01 sec)

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Counting Rows Example

A query to determine total number of pets:mysql> SELECT COUNT(*) FROM pet;+----------+| COUNT(*) |+----------+| 9 |+----------+